Small steric variations in ligands with large synthetic and structural consequences

Article abstract of DOI:10.1002/ejic.200701098

The reaction of ytterbium metal with the aminopyridines 2,6-(diisopropylphenyl)-[6-(2,6-dimethylphenyl)pyridin-2-yl]-amine (1, Ap′H) and (2,4,6-trimethylphenyl)-[6-(2,4,6-trimethylphenyl) pyridin-2-yl]amine (2, Ap^MeH) at elevated temperature under vacuum in the presence of mercury gave rise to divalent [Yb(Ap′)₂] (3) and trivalent [Yb(Ap^Me)₃] (4), respectively. The single-crystal X-ray structure analysis of 3 revealed a four-coordinate ytterbium atom with two chelating (N,N′) Ap′ ligands inclined to each other at an angle of 126.93(7)° (Cl-Yb-C26). Additionally the complex forms intermolecular C^Aryl-H agostic interactions [Yb1...C17 2.981(2) A and Yb1...H17 2.56(3) A] (all H atoms refined). Complex 4 contains a six-coordinate ytterbium atom having three chelating (N,N′) Ap^Me ligands and has distorted octahedral stereochemistry. The reaction of the potassium salts of Ap′H (5) and Ap^Me H (6) with [YbI₂ (thf)₄] in thf gave rise to the divalent lanthanoid complexes [Yb(Ap′)₂(thf)] (7), and [Yb(Ap^Me)₂(thf)₂] (8), respectively, and 7 was also obtained by redox transmetallation/ligand exchange from Yb metal, HgPh ₂ and Ap′H. X-ray crystal structures show that 7 and 8 have five- and six-coordinate ytterbium atoms and distorted trigonal-bipyramidal and distorted octahedral stereochemistry, respectively, the difference in coordination number reflecting the difference in steric demand of the Ap′ and Ap^Me ligands. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200701098

FULL PAPER
DOI: 10.1002/ejic.200701098
Small Steric Variations in Ligands with Large Synthetic and Structural
Consequences
Sadaf Qayyum,[a] Kristina Haberland,[a] Craig M. Forsyth,[b] Peter C. Junk,[b]
Glen B. Deacon,*[b] and Rhett Kempe*[a]
Keywords: Agostic interactions / Amidopyridine ligands / Aminopyridinato ligands / N ligands / Ytterbium
The reaction of ytterbium metal with the aminopyridines
2,6-(diisopropylphenyl)-[6-(2,6-dimethylphenyl)pyridin-2-yl]-
amine (1, ApЈH) and (2,4,6-trimethylphenyl)-[6-(2,4,6-tri-
methylphenyl)pyridin-2-yl]amine (2, ApMeH) at elevated
temperature under vacuum in the presence of mercury gave
rise to divalent [Yb(ApЈ)2] (3) and trivalent [Yb(ApMe)3] (4),
respectively. The single-crystal X-ray structure analysis of 3
revealed a four-coordinate ytterbium atom with two chelat-
ing (N,NЈ) ApЈ ligands inclined to each other at an angle of
126.93(7)° (Cl–Yb–C26). Additionally the complex forms
intermolecular CAryl–H agostic interactions [Yb1···C17
2.981(2) Å and Yb1···H17 2.56(3) Å] (all H atoms refined).
Complex 4 contains a six-coordinate ytterbium atom having
hedral stereochemistry. The reaction of the potassium salts of
ApЈH (5) and ApMeH (6) with [YbI2 (thf)4] in thf gave rise
to the divalent lanthanoid complexes [Yb(ApЈ)2(thf)] (7), and
[Yb(ApMe)2(thf)2] (8), respectively, and 7 was also obtained
by redox transmetallation/ligand exchange from Yb metal,
HgPh2 and ApЈH. X-ray crystal structures show that 7 and 8
have five- and six-coordinate ytterbium atoms and distorted
trigonal-bipyramidal and distorted octahedral stereochemis-
try, respectively, the difference in coordination number re-
flecting the difference in steric demand of the ApЈ and ApMe
ligands.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
three chelating (N,NЈ) ApMe ligands and has distorted octa- Germany, 2008)
Introduction
Agostic bonding has been found to play a major role in
the ligand reactivity of transition-metal complexes, particu-
larly in α-olefin polymerization.[1,2] The nature of the inter-
Scheme 1. Aminopyridinato form (left), amidopyridine form (cen-
tre) and amidinato ligands (right).
action was interpreted by Brookhart and Green in terms of
a three-centre, two-electron bond between the C–H bond
and a vacant d-orbital of the transition metal atom.[3,4] The
presence of an agostic interaction is commonly indicated by
the resulting geometric deformation of the agostic ligand,
as shown by an elongation of the C–H bond, rather short
M···H contacts, and a distortion of the ligand spatial ar-
rangement.[5,6] Aminopyridinato ligands[7,8] are of interest
due to the flexibility of their binding mode (amidopyridine
vs. aminopyridinato form)[9] and the ligand “asymmetry”.
Such ligands (Scheme 1, left) are structurally related to ami-
dinates[10] (Scheme 1, right).
We have begun investigations of very bulky versions of
such ligands.[11] Here we report that small variations in very
bulky ligands have large synthetic and structural conse-
quences including a rare example of a CAryl–H intermo-
lecular agostic interaction and a small steric range in which
such an interaction could be stabilized.
Results and Discussion
The aminopyridines 1[11a] and 2[12] [Equation (1),
Scheme 2] were prepared by palladium-catalyzed arylamin-
ation,[13] and appeared suitable for conversion into the cor-
responding (amidopyridine)lanthanoid complexes by reac-
tion of lanthanoid metals with the ligands at elevated tem-
peratures.
[a] Lehrstuhl für Anorganische Chemie II, Universität Bayreuth,
95440 Bayreuth, Germany
Fax: +49-921-55-2157
E-mail: kempe@uni-bayreuth.de
[b] School of Chemistry, Monash University,
Clayton, Victoria 3800, Australia
Fax: +61-3-99054597
E-mail: glen.deacon@sci.monash.edu.au
(1)
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S. Qayyum, K. Haberland, C. M. Forsyth, P. C. Junk, G. B. Deacon, R. Kempe
FULL PAPER
Scheme 2. 2,6-Dialkylphenyl-substituted aminopyridines and the
numbering scheme used for NMR assignments.
This “direct” synthetic method[14] is especially valuable
for homoleptic lanthanoid organoamides and phenolates[15]
and has recently been extended to analogous alkaline earth
complexes.[16] Direct reaction of 1 with ytterbium metal ac-
tivated by mercury metal under vacuum at 250 °C gave rise
to divalent [Yb(ApЈ)2] (3) (Scheme 3). Mercury assists by
way of metal surface amalgamation/cleaning, while the
molten ligand possibly acts initially as a solvent until the
reaction mixture solidifies.
Figure 1. Molecular structure of [Yb(ApЈ)2] (3). Hydrogen atoms
are omitted for clarity. Selected bond lengths [Å] and angles [°]:
N1–Yb1 2.4323(18), N2–Yb1 2.4041(18), N3–Yb1 2.3708(18), N4–
Yb1 2.4489(18); N1–Yb1–N2 56.05(6), N1–Yb1–N3 105.89(6),
N1–Yb1–N4 151.90(6), N2–Yb1–N3 116.20(6), N2–Yb1–N4
109.36(6), N3–Yb1–N4 56.02(6), C1–Yb1–C26 126.93(6).
This open sandwich structure leaves a vacant face on the
Yb atom. To compensate for this, there is a close contact
between a carbon–hydrogen bond of one of the phenyl rings
of one YbApЈ2 molecule and a neighbouring Yb atom, with
Yb1···C17 bonding distances of 2.981(2) Å and Yb1···H17
distances of 2.56(3) Å (all H atoms refined; Figure 2). Steri-
cally crowded homoleptic (NacNac)YbII complexes adopt
a highly symmetric non-bent structure.[20] Thus, we con-
clude that for anionic bidentate N,N ligands the thermody-
namically more stable form is the highly symmetric and not
the bent conformation. The ligand inclination may result
from these unique intermolecular agostic interactions.
Structurally characterized mononuclear homoleptic (amidi-
nato/aminopyridinato/amidopyridine)YbII complexes have
not yet been described to the best of our knowledge.
Scheme 3. Synthesis of the ytterbium complexes 3 and 4.
Suitable crystals of 3 could be grown during the complex
synthesis. For crystallographic details see Table 1. The mo-
lecular structure of divalent homoleptic 3 (Figure 1) exhib-
its a bent structure as observed for the metallocenes [Yb{η-
C5H3(1,3-SiMe3)2}2][17] and [Ln(η-C5Me5)2] (Ln = Sm,[18,19]
Eu[19]). The C1–Yb–C26 angle for 3 is 126.93°, rather small
when compared with the centroid–Yb–centroid angle of
bulky [Yb{η-C5H3(1,3-SiMe3)2}2] (138.0°). The ytterbium
atom is four-coordinate with two chelating ApЈ ligands. The
Figure 2. X-ray structure of 3 showing intermolecular agostic inter-
actions [Yb1···C17 2.981(2), Yb1···H17 2.56(3) Å].
Reduction of the steric bulk, by applying 2 – a ligand
Yb–N bond lengths suggest that both ligands are in the which is smaller than 1 – according to Equation (1) led to
amidopyridine form. a trivalent homoleptic Yb complex (Scheme 3). The forma-
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Small Steric Variations in Ligands with Large Consequences
Table 1. Details of the X-ray crystal structure analyses of 3, 4, 7 and 8.
3
4
7·2C7H8
7·0.5C6H14
8·C6H14
Empirical formula
Formula mass
Crystal system
Space group
a [Å]
b [Å]
c [Å]
C50H58N4Yb
888.04
monoclinic
P21/c
12.1463(3)
22.6968(6)
15.5101(4)
90
95.608(1)
90
C69H75N6Yb
1161.39
C68H82N4OYb
1144.42
monoclinic
P21/n
11.1460(7)
27.6330(19)
19.960(15)
90
103.037(5)
90
5991.3(7)
4
C57H73N4OYb
1003.23
monoclinic
P21/c
10.8483(2)
24.2933(5)
19.7081(3)
90
101.643(1)
90
5087.02(16)
4
C30H40N2OYb
531.16
monoclinic
P2/c
12.4800(7)
12.2840(8)
18.6520(12)
90
104.689(5)
90
triclinic
¯
P1
11.4580(7)
11.4970(7)
26.6150(18)
101.131(5)
90.670(5)
118.141(4)
3011.8(3)
2
α [°]
β [°]
γ [°]
V [Å3]
4255.39(19)
4
2766.0(3)
4
Z
Crystal size [mm]
ρcalcd. [gcm–3]
µcalcd. [mm–1] (Mo-Kα)
T [K]
θ range [°]
No. of obsd. refl. [I Ͼ 2σ(I)] 11605
0.18ϫ0.10ϫ0.08
1.386
2.236
123(2)
1.60–30.00
0.19ϫ0.18ϫ0.17
1.281
1.598
193(2)
1.57–25.82
5573
0.17ϫ0.15ϫ0.10
1.269
1.605
193(2)
1.28–25.85
6844
0.25ϫ0.25ϫ0.25
1.310
1.880
123(2)
2.51–27.50
10516
0.39ϫ0.17ϫ0.11
1.276
1.734
193(2)
1.66–25.71
3364
No. of unique refl.
No.of parameters
R [IϾ2σ(I)]
wR2
12400
728
0.0321
0.0590
11144
685
0.0606
0.1193
11392
667
0.0408
0.0993
11681
581
0.0379
0.0793
5237
303
0.0447
0.0860
tion of bis- or tris(amidopyridine)ytterbium complexes and
It is noteworthy that the ligands are coordinated in the
thus the formation of di- or trivalent complexes can be ex- amidopyridine binding mode to the metal atom. The dif-
plained in terms of the steric bulk of the corresponding li- ferent bond lengths for Yb–N1pyridine [2.357(8) Å] and Yb–
gands. The rare earth metal atom can bind three ligands of N2amido [2.264(7) Å] indicate an amidopyridine binding
the less bulky version, ApMe, and thus the thermodynami- mode where the anionic function is localized at the amido
cally favoured trivalent oxidation state is accessible. Ytter- N-atom. A similar situation is noticeable with the bond
bium can only bind two ligands of the slightly bulkier ver- length Yb–N5pyridine [2.543(7) Å] and Yb–N6amido
sion, and thus the redox process stops at the oxidation state [2.299(7) Å]. The ligand N3,N4 is also in the amidopyridine
of two. X-ray analysis of 4 (for crystal and refinement data, form, but the difference in appropriate bond lengths is
see Table 1) reveals a distorted octahedral coordination for smaller (0.13 Å). It is noteworthy that, for one of the li-
the ytterbium atom (Figure 3).
gands, the Yb–Npyridine bond (2.543 Å) is much longer than
the averaged Yb–Npyridine bond for the two others (2.376 Å)
indicating weak bonding due to steric saturation. Ligands
N3,N4 and N1,N2 are the ligands containing the respective
donor atoms.
Salt metathesis reactions of 5 (potassium salt of 1)[11a]
with [YbI2(thf)4] in thf solution resulted in the formation
of the bis(amidopyridine)YbII complex 7 (Scheme 4). In ad-
dition, 7 was prepared from Yb metal by redox transmetal-
lation/ligand exchange in thf [Equation (2)].
(2)
Figure 3. Molecular structure of [Yb(ApMe)3] (4). Selected bond
lengths [Å] and angles [°]: N1–Yb1 2.357(8), N2–Yb1 2.264(7), N3–
Yb1 2.395(7), N4–Yb1 2.263(7), N5–Yb1 2.543(7), N6–Yb1
2.299(7); N4–Yb1–N2 106.1(2), N4–Yb1–N6 158.4(2), N2–Yb1–
N6 95.5(3), N4–Yb1–N1 92.5(3), N2–Yb1–N1 58.4(3), N6–Yb1–
N1 98.7(2) N4–Yb1–N3 59.0(3), N2–Yb1–N3 98.9(3), N6–Yb1–
N3 118.7(3), N1–Yb1–N3 138.8(2), N4–Yb1–N5 102.1(2), N2–
Yb1–N5 151.2(2), N6–Yb1–N5 56.3(2), N1–Yb1–N5 115.6(2), N3– Scheme 4. Synthesis of 7 and 8 (5, 7: n = 1, R = iPr; RЈ = H; 6, 8:
Yb1–N5 100.2(2).
n = 2, R = RЈ = Me) by metathesis reactions.
Eur. J. Inorg. Chem. 2008, 557–562
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S. Qayyum, K. Haberland, C. M. Forsyth, P. C. Junk, G. B. Deacon, R. Kempe
FULL PAPER
X-ray quality crystals of 7·2C7H8 were grown from con-
centrated toluene solution. In addition, crystals of
7·0.5C6H14 were grown from hexane. In the case of the ste-
rically more demanding ligand ApЈ, only one thf molecule
coordinates to the central metal atom. The resulting five-
coordination can be best described as very distorted trigo-
nal-bipyramidal, with the N2, N4 and O1 atoms in the Yb
plane and N1 and N3 apical [N1–Yb1–N3 157.59(14)°]
(Figure 4). The Yb–Npyridine [2.479(4), 2.466(4) Å] bonds
are significantly longer than the Yb–Namido bonds
[2.380(4), 2.384(3) Å] indicating an amidopyridine bonding
mode.
Figure 5. Molecular structure of [Yb(ApMe)2(thf)2] (8). Hydrogen
atoms and hexane molecule are omitted for clarity; selected bond
lengths [Å] and angles [°]: N1–Yb1 2.544(4), N2–Yb1 2.396(5), O1–
Yb1 2.428(4); N2–Yb1–N2A 105.7(2), N2–Yb1–N1 54.76(15),
O1A–Yb1–O1 78.1(2).
54.76°) underlines the strained nature of the amidopyridine
ligand binding. The Yb–Npyridine and Yb–Othf bonds of 8
are longer than those of 7 by amounts consistent with a
change of one in the coordination number,[22] but the differ-
ences in the Yb–Namido distances is much smaller (ca.
0.02 Å).
The nature of the products depends highly on the size of
the ligands as the steric bulk is in the order Ap*–H Ͼ ApЈ–
H Ͼ ApMe–H. In the present study, the formation of the
solvent-free complexes 3 and 4 has been enforced by the use
of solvent-free conditions. The smallest ligand, ApMe–H,
yields a six-coordinate YbIII complex, and the slightly bulk-
ier ApЈ–H yields a 4-coordinate YbII complex with rare
intermolecular agostic interactions. This indicates that the
coordination sphere is large enough to induce the presence
of an agostic interaction but not large enough to accommo-
date a third ligand. Agostic complexes are often unstable,
and substrate coordination and/or chelation generally seem
to be necessary to bring the C–H bond and the coordina-
tively unsaturated metal centre into close proximity.[23] The
reaction of the sterically more demanding aminopyridine
Ap*–H (9), {(2,6-diisopropylphenyl)[6-(2,4,6-triisopropyl-
phenyl)pyridin-2-yl]amine}[11a] directly with Yb metal
mainly gave starting material. Salt metathesis reactions of
the potassium salt of 9 with [YbI2(thf)4] in thf solution re-
sulted in the formation of a heteroleptic ytterbium iodide
dimer [Yb2(Ap*)2I2(thf)4],[11b] notably with an Ap*/Yb ra-
tio of 1:1. This outcome is driven by the extreme bulk of
Ap* and contrasts the present metathesis reactions
(Scheme 4).
Figure 4. Molecular structure of [Yb(ApЈ)2(thf)] (7). Hydrogen
atoms and two toluene molecules are omitted for clarity; selected
bond lengths [Å] and angles [°]: N1–Yb1 2.479(4), N2–Yb1
2.380(4), N3–Yb1 2.466(4), N4–Yb1 2.384(3), O1–Yb1 2.362(4);
N4–Yb1–N1 113.38(15), O1–Yb1–N1 101.37(15), O1–Yb1–N4
114.73(16), N3–Yb1–N1 157.59(14), N4–Yb1–N3 55.82(15), O1–
Yb1–N3 101.05(15), N2–Yb1–N1 56.17(14), N2–Yb1–N4
126.99(15), O1–Yb1–N2 118.28(16), N2–Yb1–N3 112.02(16).
The reactant 6 was prepared in a similar fashion to 5[11a]
and was treated with [YbI2(thf)4] in thf. Product 8 was ex-
tracted with hexane, and crystallisation afforded red crys-
tals. Complex 8 was characterized by X-ray crystal-struc-
ture analysis and contains one hexane molecule per Yb
atom in the crystal lattice. Crystal and refinement details
are listed in Table 1. The molecular structure of 8 is shown
in Figure 5.
The reduction of the steric bulk of the amidopyridine
from 7 to 8 allows for the coordination of the two thf li-
gands which bind to the metal centre in a cisoid manner,
and the coordination arrangement can be best described as
distorted octahedral. The Yb–Npyridine (2.544 Å), Yb–
Namide (2.396 Å) and Yb–O distances are comparable to
other related thf complexes,[11b] and the bonding mode is
amidopyridine in character. Considering the lability of the
coordinated thf molecules, it is surprising that the Yb–O
distance (Figure 5) lies close to the mean value for those in
all previously reported Yb–Othf interactions (2.43 Å).[21]
Conclusions and Outlook
The direct reaction between lanthanoid metal and bulky
The small chelating angle Namido–Yb–Npyridine (average aminopyridines is an effective and simple way to synthesize
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Small Steric Variations in Ligands with Large Consequences
(C6D6, 298 K, paramagnetic species): δ = –5.20 (br. s), 1.11 (d),
2.19 (m), 11.96 (s), 20.17 (s), 34.95 (br. s), 67.05 (br. s) ppm.
true homoleptic “monomeric” amidopyridine complexes of
Yb. The complexes predominantly adopt the amidopyridine
binding mode. Relatively less bulky 2 results in the forma-
tion of a six-coordinate trivalent Yb complex, whereas
more bulky 1 afforded a low-coordinate divalent Yb com-
Synthesis of [(ApMeK)] (6): ApMeH, (3.00 g, 9.08 mmol), and KH
(0.364 g, 9.08 mmol) were placed into a Schlenk flask in a glove
box. Diethyl ether (50 mL) was added to this mixture at 0 °C. The
pound showing intermolecular CAryl–H agostic interac- yellow reaction mixture was stirred at room temperature overnight,
then filtered and the solvent removed in vacuo to dryness. The
resulting yellow precipitate was washed with hexane and then dried
under vacuum. Yield (3.240 g, 97%). C23H25KN2 (368.56): calcd.
tions, which do not persist in thf, from which five-coordi-
nate [Yb(ApЈ)2(thf)] (7) is isolated. A further increase of the
steric bulk leads to different chemistry, such as mixed
amido/iodo complexes in salt metathesis chemistry. Further
studies are directed towards the exploration of the differ-
ences in reactivity of the low-valent ytterbium complexes
introduced here.
1
C 74.95, H 6.84, N 7.60; found C 74.70, H 6.73, N 7.03. H NMR
(C6D6, 298 K): δ = 2.02 [s, 6 H, H13,14,22,24 o-Me], 2.17 [s, 6 H,
H13,14,22,24 o-Me], 2.24 [s, 3 H, H15 or 23 p-Me], 2.33 [s, 3 H,
H
15 or 23 p-Me], 5.74 [dd, 1 H, H3 or 5 m-H(py)], 5.77 [dd, 1 H, H3 or 5
m-H(py)], 6.85 [s, 2 H, H18,20 H(Ar)], 6.96 [s, 2 H, H9,11 H(Ar)],
6.98 [t, 1 H, H4 p-H(py)] ppm. 13C NMR (C6D6, 298 K): δ = 19.2
(d, C13,14,22,24), 20.1 (d, C13,14,22,24), 20.9 (C15,23), 21.2 (C15,23), 103.9
(d, C3/5), 105.4 (d, C3/5), 129.3 (d, C9,11), 129.4 (C19), 129.5 (C18,20),
131.2 (C17,21), 135.2 (C8,12), 135.5 (C7), 138.1 (C10), 140.1 (C22),
141.3 (C4), 158.4 (C6), 165.5 (C2) ppm.
Experimental Section
General Procedures: All reactions and manipulations with air-sensi-
tive compounds were performed under dry argon or N2, using stan-
dard Schlenk and glovebox techniques. Non halogenated solvents
were distilled from sodium/benzophenone. Deuterated solvents
were obtained from Cambridge Isotope Laboratories and were de-
gassed, dried and distilled from sodium/benzophenone prior to use.
All chemicals were purchased from commercial vendors and used
without further purification. Ytterbium metal was obtained from
Santoku. NMR spectra were obtained using either a 250 or
400 MHz Bruker ARX spectrometer. Chemical shifts are reported
in ppm relative to the deuterated solvent. X-ray crystal structure
analyses were performed with a STOE-IPDS II or an Enraf–Non-
ius KAPPA CCD diffractometer equipped with a low-temperature
unit. Structure solution and refinement were accomplished using
SIR97,[24] SHELXL-97[25] and WinGX.[26] Crystallographic details
are summarised in Table 1. Elemental analyses were carried out
with Vario Elementar EL III or Leco CHNS-932 elemental ana-
lysers. CCDC-663340 to -663344 contain the supplementary crys-
tallographic data for this paper. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Synthesis of [Yb(ApЈ)2(thf)] (7). Method I (Toluene Co-Crystallized):
YbI2(thf)4 (1.072 g, 1.50 mmol) and 4 (1.10 g, 3.00 mmol) were
placed into a Schlenk flask in a glove box; thf (40 mL) was added
to the dark maroon-coloured reaction mixture which was stirred
overnight. The solvent was evaporated under vacuum. The product
was extracted with toluene (30 mL). The mixture was filtered and
the filtrate concentrated to afford dark red crystals suitable for X-
ray analysis after 24 h at –20 °C. Yield (0.600 g, 45%).
C54H66N4OYb (960.17): calcd. C 67.55, H 6.93, N 5.84; found C
1
66.99, H 6.76, N 5.65. H NMR (C6D6, 298 K): δ = 1.13 [d, 12 H,
H22,23,25,26 Me2(CH)], 1.29 [br. m, 16 H, H22,23,25,26 Me2(CH), β-
CH2, thf], 1.90 [s, 12 H, H13,14 Me(Ar)], 3.41 [br. s, 8 H, H21,24, α-
CH2, thf], 5.70 [dd, 2 H, H3 m-H(py)], 6.82 [dd, 2 H, H5 m-H(py)],
6.96 [t, 2 H, H4 p-H(py)], 7.26–7.32 [m, 12 H, H9,10,11,17,18,19 H(Ar)]
ppm. 13C NMR (C6D6, 298 K): δ = 19.8 (d, C13,14), 24.5
(C22,23,25,26), 24.8 (C22,23,25,26), 25.5 (Cβ-thf), 28.4 (C21,24), 31.9
(C21,24), 68.0 (Cα-thf), 105.9 (C3/5), 123.4 (C17,19), 123.8 (C9,11), 128.2
(C18), 135.8 (C10), 138.2 (C16,20), 142.2 (C7), 142.3 (C4), 143.5 (C15),
146.9 (C8,12), 155.8 (C6), 168.9 (C2) ppm. Analysis and NMR sam-
ples toluene-free. Method II (Hexane Co-Crystallized): A mixture
of Yb metal (1.04 g, 6.0 mmol), HgPh2 (0.71 g 2.0 mmol) and
ApЈH (1.37 g, 4.0 mmol) in thf (40 mL) was heated to 65 °C while
being stirred for 24 h. After cooling, the reaction mixture was fil-
tered and the red-orange solution concentrated to dryness.
Recrystallization of the residue from hexane gave the title com-
pound as red needles Yield (1.24 g, 62%). 1H NMR (C6D6, 298 K):
δ = 0.94 [m, 2 H, CH2 (hexane)], 1.14 [br. s, 12 H, H22,23,25,26
Me2(CH)], 1.27 [br. m, 21 H, H22,23,25,26 Me2(CH), β-CH2, CH2/
CH3(hexane)], 1.88 [br. s, 12 H, H13,14 Me(Ar)], 3.40 [br. s, 8 H,
Synthesis of [Yb(ApЈ)2] (3): ApЈH (0.50 g, 1.4 mmol), Yb powder
(0.40 g, 2.31 mmol) and a drop of mercury metal were heated to-
gether at 250 °C in a vacuum-sealed glass tube for 16 d. The glass
tube was gradually cooled to room temperature. After cooling,
some red crystals of [Yb(ApЈ)2] were observed and handpicked for
X-ray crystallography. Yield (0.476 g, 77%). C50H58N4Yb (888.04):
1
calcd. C 67.62, H 6.58, N 6.31; found C 68.13, H 6.40, N 5.87. H
NMR (C6D6, 296 K): δ = 1.04 [br. d, 12 H, H22,23,25,26 Me2(CH)],
1.32 [br. d, 12 H, H22,23,25,26 Me2(CH)], 1.56 [br. s, 6 H, H13,14
Me(Ar)], 2.11 [br. s, 6 H, H13,14 Me(Ar)], 3.41 [br. m, 4 H, H21,24],
5.60 [d, 2 H, H3 m-H(py)], 5.67 [dd, 2 H, H5 m-H(py)], 6.72 [t, 2
H, H4 p-H(py)], 7.26–7.32 [m, 12 H, H9,10,11,17,18,19 H(Ar)] ppm.
13C NMR (C6D6, 298 K): δ = 19.6 (s, C13,14), 24.3 (C22,23,25,26),
25.3 (C22,23,25,26), 25.8 (s, C13,14), 25.71 (C21,24), 27.5 (C21,24), 96.94
(C3 or 5), 106.73 (C3 or 5), 123.51 (C17,19), 123.73 (C9,11), 124.4 (C18),
137.1 (C10), 138.0 (C16,20), 142.6 (C7), 143.1 (C4), 145.4 (C15), 146.8
(C8,12), 155.5 (C6), 169.1 (C2) ppm.
3
4
H21,24, α-CH2, thf], 5.71 [dd, J = 6.9, J = 0.9 Hz, 4 H, H3 or 5 m-
H(py)], 6.81 [br. s, 6 H, H17,18,19 H(Ar)], 6.99 [br. m, 2 H, H4 p-
H(py)], 7.29 [br. m, 6 H, H9,10,11 H(Ar)] ppm.
Synthesis of [Yb(ApMe)2(thf)2] (8): [YbI2(thf)4] (1.072 g, 1.50 mmol)
and 6 (1.100 g, 3.00 mmol) were placed into a Schlenk flask in a
glove box; thf (40 mL) was added to the reaction mixture being of
dark maroon colour at the time of addition. The reaction mixture
was stirred overnight. The solvent was removed under vacuum, and
hexane (30 mL) was added. The mixture was filtered and the filtrate
concentrated to afford dark red crystals suitable for X-ray analysis
after 24 h at –20 °C. Yield (1.00 g, 85.57%). C54H66N4O2Yb·C6H14
(1062.34): calcd. C 67.84, H 7.59, N 5.27; found C 67.57, H 7.87,
Synthesis of [Yb(ApMe)3] (4): Yb powder (0.262 g, 1.51 mmol), Ap-
MeH (0.500 g, 1.51 mmol), and mercury metal (two drops) were
heated together at 250 °C in a vacuum-sealed glass tube for 9 d.
The glass tube was gradually cooled to 150 °C over 1 d, and further
cooling to room temperature yielded light orange crystals of [Yb-
(ApMe)3]. Yield (0.200 g, 60%). C69H75N6Yb (1161.41): calcd. C
1
N 5.72. H NMR (C6D6, 298 K): δ = 1.23 (br. s, 8 H, β-CH2, thf),
71.36, H 6.51, N 7.24; found C 72.02, H 7.35, N 6.92. 1H NMR 2.05 (s, 12 H, H13,14,22,24 o-Me), 2.12 (s, 6 H, H15,23 p-Me), 2.20 (s,
Eur. J. Inorg. Chem. 2008, 557–562
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561

S. Qayyum, K. Haberland, C. M. Forsyth, P. C. Junk, G. B. Deacon, R. Kempe
FULL PAPER
12 H, H13,14,22,24 o-Me), 2.38 (s, 6 H, H15,23 p-Me), 3.33 (br. s, 8 H,
α-CH2, thf), 5.81 [dd, 4 H, H3/5 m-H(py)], 6.69 [s, 4 H, H18,20
H(Ar)], 6.93 [t, 2 H, H4 p-H(py)], 6.96 [s, 4 H, H9,11 H(Ar)] ppm.
13C NMR (C6D6, 298 K): δ = 19.2 (d, C13,14,22,24), 20.1 (d,
C13,14,22,24), 21.2 (C15,23), 23.0 (C15,23), 25.4 (β-CH2, thf), 68.3 (α-
CH2, thf), 105.9 (d, C3/5), 105.7 (d, C3/5), 129.3 (d, C9,11), 130.0
(C18,20), 132.5 (C17,21), 135.8 (C19), 136.1 (C8,12), 137.9 (C7), 138.1
(C10), 140.1 (C22), 147.5 (C4), 156.3 (C6), 167.9 (C2) ppm.
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Attempted Synthesis of [Yb(Ap*)2] (10): Yb powder (0.189 g,
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Acknowledgments
Financial support from the Deutsche Forschungsgemeinschaft
(Schwerpunktprogramm 1166 “Lanthanoid-spezifische Funktiona-
litäten in Molekül und Material), the Fonds der Chemischen Indus-
trie and the Australian Research Council is gratefully acknowl-
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Received: October 11, 2007
Published Online: December 7, 2007
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